Cellular communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive phone calls most anywhere they travel. Moreover, as cellular telephone technology is increased, so too has the functionality of cellular devices. For example, many cellular devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, etc. These multi-function devices usually allow users to wirelessly send and receive electronic mail (email) messages and access the internet via a cellular network and/or a wireless local area network (WLAN), for example.
As the functionality of cellular communications devices continues to increase, so too does demand for smaller devices that are easier and more convenient for users to carry. As any circuit boards and electronic components thereon are reduced in size and placed closer together, including antenna and microphone components, various electronic components can pick up conductive energy and create interference within the system.
Many of the designs include an RF metal shield secured onto the printed circuit board, and surrounding and isolating different RF components, including transceiver chip sets such as multi-chip modules, which are secured on the circuit board within the housing. The RF metal shield encloses these components and chip sets. Some of the RF components or chip sets radiate RF energy to other chips or components that are in close proximity from electromagnetic coupling through the RF metal shield. This type of electromagnetic coupling (EMC) or electromagnetic interference (EMI) coupling causes interference to the RF circuits, and degrades RF performance, such as receiver sensitivity. Thus, the RF metal shield that is supposed to shield the components from extraneous RF energy can in and of itself create electromagnetic coupling problems with different RF components that are supposed to be shielded within the RF shield.